1. Field of the Invention
This invention relates in general to a cold cathode fluorescent lamp device, and in particular, to a high luminance, high efficiency, long lifetime monochromatic, multi-color or full-color cold cathode fluorescent lamp devices (CFD).
2. Description of the Prior Art
Hot cathode fluorescent lamps (HCFLs) have been used for illumination. The HCFL operates in the arc gas discharge region. It operates at a relatively low voltage (of the order of 100 volts), large current (in the range of 60 milliamps), high efficiency (such as 80 lm/W, and the cathode is usually operated at a relatively high temperature such as 400 C. Typically, the cathodes would first need to be heated to an elevated temperature by means of a starter and a ballast before the HCFL may be turned on and operated at its optimum temperature. Thus, in order to turn on an HCFL, a voltage is applied to the starter which generates gas discharge. The heat produced by the gas discharge heats up the cathode and an electron emission layer on the cathode to an elevated temperature so that the layer emits electrons to maintain the gas discharge. The gas discharge generates ultraviolet radiation which causes a phosphor layer in the lamp to emit light.
When the cathode and the electron emission layer are first heated to an elevated temperature during starting, the heating causes a portion of the electron emission layer to evaporate, so that after the HCFL has been started a number of times, the electron emission layer may become deficient for the purpose of generating electrons, so that the HCFL needs to be replaced. This problem is particularly acute for displaying information that requires constant starting and turning off the HCFLs. Thus, HCFLs are not practical for use in computer, video, and television applications. For the purpose of illumination, HCFLs requires starters and ballasts, which may also become defective after a period of constant use. This also reduces the lifetime of the HCFL. It is thus desirable to provide an illumination device with improved characteristics.
Currently available traffic light and outdoor large size sign displays are normally made of incandescent lamps. They have high brightness, but many drawbacks:
a. High maintenance cost because of short lifetime and low reliability. This is the case especially for traffic lights or signs on free ways, where changing and repair of the lights are very inconvenient and expensive. PA1 b. High power consumption because of low luminous efficiency, which is about 10 lm/W. For traffic lights and other multi-colored displays, luminance efficiency is even lower because colored light is obtained by filtering white light emitted from the incandescent lamps, so that the colored fight so obtained is much reduced in intensity. The effective efficiency for such applications is only 4 lm/W or lower. PA1 c. Under direct sunight, ON/OFF contrast is very low, i.e., even OFF status looks like ON, which can cause fatal results.
It is, therefore, desirable to provide an improved illumination device which avoids the above-described disadvantages.